Ch. 16 Innate Immunity: Nonspecific Defenses of the Host Flashcards
Mechanisms of the innate immunity
Its a “standing army” and its functions are more general than specific.
1st line defense
Skin, m membranes, etx. sometimes breached
2nd line of defense
Fever, inflammation
3rd line of defense
humoral and cell immunity
1st line defenses
Physical, chemical, normal microbiota. mucous (entraps microbes to flush them out). tears (prevent pathogens from attaching to eyes).
Normal microbiota
- Perform microbial antagonism.
- Compete for nutrients and crowd out pathogens.
- Some produce substances that are harmful to pathogens.
- they alter environment. pH for example.
- necessary for the development of the immune system. Hygiene hypothesis.
Phagocytosis
- Neutrophils and macrophages.
Steps of phagocytosis (step 1)
- Phagocyte attaches to pathogen. Bacteria has to have receptors on it (ligands) for the phagocyte to recognize it.
side note: PRRs pattern recognition receptors = recognize attributes of bacteria that human cells do not have. Like peptidoglycan and flagellum.
side note 2.0: Pathogen associated molecular pattern (PAMPs) are these patterns that phagocytes recognize.
Capsules can inhibit recognition of these PAMPs.
Steps of phagocytosis (step 2)
- Engulfment. Bacteria in a vesicle inside cytoplasm. Cytosome. Lysozomes fuse with phagosome to become a phagolysozome. Then pathogen is “digested”.
Steps of phagocytosis (step 3)
- Bits and pieces of pathogen get dumped outside of cell.
Inflammation
- Response to tissue damage.
- Brings effectors to site of infection that help with tissue repair
A series of responses in inflammation
- Clears infection and repairs. increases blood flow and anti-microbes
- Typically localized inflammation
Systemic infection
- Fever
- Bacterial endotoxins (pyrogens) (lipid A)
- IL-1 and TNF - a
Complement initiation – results of complement activation
Its a series of 9 proteins that are always in an inactive form (1 - 9). They are activated when an acute infection occurs. So its innate.
3 pathways – classical pathway
Discovered first. Only know step one –>
antibodies bind to antigen and it starts. Plays later in immune response. the three pathways work together.
Alternative pathway
Discovered 2nd. Plays in before use of antibodies. Factor B,D, and E bind to antigens on microbe. Complement then binds to those proteins.
Lectin pathway
Binds to a carbohydrate. MBL binds to carbs on bacteria cell surface. Allows binding of complement proteins.
Outcomes of complement pathways
- Cytolysis. bursting of gram-neg bacteria.
- Opsonization: an immune process which uses opsonins to tag foreign pathogens for elimination by phagocytes.
- Inflammation. Complement proteins promote it. Blood vessels become more permeable. Binding on mast cells to release granules like histamine to assist.
Interferons
Interfere with viruses. there is an alpha and beta verions. a-INF and b-INF. Any cell can make these a & b INFs. Once a cell is infected these don’t help, and they don’t cure the infected cell.
INFs.
Slow the spread of viral infections by protecting neighboring cells.
How does a cell know its infected, and to produce INFs?
Long double strand RNA in host cytoplasm produced during virus life cycle alerts it
The process of INFs alerting neighboring cells (fig 16.14)
- Viral DNA from an infecting virus enters the cell
- The virus induces the host cell to produce interferon mRNA (INF-mRNA), which is translated into alpha and beta interferons.
- Interferons make contact with uninfected neighboring host cells, where they bind either to the plasma membrane or to nuclear receptors. Interferons induce the cells to synthesize antiviral proteins (AVPs).
- AVPs degrade viral mRNA and inhibit protein synthesis – and thus interfere with viral replication.
Iron binding proteins
- Competition with pathogens
- Antimicrobial peptides (AMPs) triggered by carbs/proteins on microbes.
Modes of action
- Inhibiting cell wall synthesis
- Forming pores in the p-membrane leading to lysis
- destroying DNA and RNA (but not destroying our microbiota)
- The trigger to these things is the binding of foreign cells to our own cells
- This innate immune system works with the adaptive immune system.
